Numerous fluoroplastics such as TEFLON, e.g., PTFE, and PFA, have been widely used for coatings, electrical insulation and as structural components due to their superior properties in the areas of hydrophobicity, chemical and thermal stability and electrical insulation. While these materials have grown in popularity, presently adhesive bonding problems are often encountered when attempting to bond these fluoroplastic materials to surfaces of other bodies.
Fluoroplastics are insoluble, nonpolar, and have low surface energy. These unique properties, which are beneficial for many applications, make the material surface generally non-wettable, and consequently generally non-bondable in the untreated surface condition. Because TEFLON and other fluoroplastics are noted for their chemical inertness, some special and strong methods have been required for surface treatment. Plasma surface treatment has been attempted, but its effectiveness is minimal and unreliable. The present conventional surface treatment for TEFLON involves the use of a chemical etching agent, prior to the application of an adhesive, which contains a sodium-naphthalene complex. The agent is corrosive and may be hazardous in use. Accordingly, in many applications, the use of such an agent is undesirable or impracticable. The required etching action has to be drastic enough to convert the TEFLON surface from nonpolar to polar. After such a conversion, the etched surface layer is so much different from the bulk of the polymer that the molecular bond of the etched layer to the bulk of the polymer is significantly weakened. This weak bondline is subject to moisture penetration and layer separation when bonded with an adhesive, without regard to any superior characteristics of the adhesive employed. In any event, the extent and nature of the etch is critical in terms of the initial initial bond strength. The etched surface is sensitive to moisture, oxygen and UV light, and the bond strength may significantly deteriorate over a period of time with environmental exposure.